#9858: Typeable instances should be kind-aware -------------------------------------+------------------------------------- Reporter: dreixel | Owner: Type: bug | Status: merge Priority: highest | Milestone: 7.10.2 Component: Compiler | Version: 7.9 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | typecheck/should_fail/T9858a, | should_run/T9858b | Blocking: | Differential Revisions: Phab:D652 -------------------------------------+------------------------------------- Comment (by simonpj): In conversation we had the staggeringly lovely idea of writing a bunch of classes thus: {{{ class (c1,c2) => (,) c1 c2 class (c1,c2,c3) => (,,) c1 c2 c3 }}} etc. I have written the class constructors prefix to stress that we are defining a ''class'' `(,)` etc, but we could equally well say {{{ class (c1,c2) => (c1,c2) -- Ha ha ha }}} Now the point is this: * `c1` and `c2` are simply superclasses of the class `(c1,c2)`. * The defined class `(,)`, of course, has kind `Constraint -> Constraint -> Constraint`. * This class is distinct from the data type `(,)`. It is just spelled the same way (confusingly perhaps, but that ship has sailed). * All the usual rules for superclasses apply. If you have the class `(c1,c2)` then you can extract the superclasses `(c1,c2)`. * If you grep for `TuplePred` in GHC you'll find quite a bit of code. All of this can be deleted; the existing superclass machinery will do the job just fine. I like this. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9858#comment:95 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler